How to Sweat (solder) Copper Pipe





Introduction: How to Sweat (solder) Copper Pipe

I had a plumbing problem needing to be addressed (people: stop mixing copper with cast iron piping!) and learned how to sweat (solder) copper piping. Why do they call it sweating instead of soldering? I have no idea, since I'm not a plumber, but I've done a decent enough job at sweating the copper that I have no leaks in my basement (anymore).

I don't know everything, as you'll see I'm a little short on details, good tips, good practices, background info, or plumbing code (did I mention I'm not a plumber). But hopefully it's good enough to get you started on your next project. Have fun!

Step 1: Start With a Freshly Cut Copper Pipe.

Depending how bad you cut the pipe (the best thing I had at the time was an angle grinder), you'll end up with a crappy looking end with burrs.

Step 2: Deburr the Pipe End.

I used the angle grinder to remove the burrs on the outside of the pipe, and then used a multi-step drill bit to remove the burrs on the inside.

Step 3: Sand the Outside

Use some plumbers fabric to clean the outside of the pipe. You could try sandpaper, but the plumbers fabric is really abrasive, works well, and it's cheap.

Step 4: Ream the Inside.

Ream the inside of the pipe with a pipe cleaner. Make sure you buy the appropriately sized cleaner for your pipe.

Step 5: Apply Flux

Buy a flux on the with a wide temperature range, especially if you're a newbie like me. I used the Oatey No.95 flux. Apply it on the outside of the pipe. Non-disclaimer: I am not affiliated with Oatey by any means.

Step 6: Install Fitting, Then Apply Heat and Solder :)

Finally, the fun part (the part with fire).

After installing the fitting (note: ream the fitting with a pipe cleaner too!), start applying heat. Move the torch around to "evenly" heat the mating area. After a subjectively short amount of time, try applying the solder to pipe. Don't just put the solder in the flame for it to melt, you want the pipe to melt the solder.

Once the solder melts around the joint and starts pool at the bottom, you're finished (it takes very little solder to do this). Do a quick check around pipe to make sure solder flowed all around it.

After it's cooled, clean off the leftover flux with soap and water. Then hope you have no leaks.



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    no no no! all these power tools are more likely to cause damage to the soft copper pipe than spending $10 for a pipe cutter, available at any hardware store:
    even if it seems like you have good cuts/smooth surfaces with these crazy power tools, i would wager that the soldered seal you make is more likely to fail than if cut cleanly with a pipe cutter.
    also, don't clamp the soft copper pipe with vise grips as shown; again, you are likely to deform the pipe/push it out of round.
    the pipe really is softer than you might imagine. for this reason, always cut half an inch off the end of new pipe, because odds are it has been dented slightly out of round somewhere in the supply chain scheme.
    i would also like to emphasize that it's imperative that both pipe and fitting are sanded/brushed until they are super shiny - they need to be for full adhesion of the solder.
    the "subjectively short amount of time" is actually precipitated by a change in flame color, so you will have some visual warning. the flame turns kind of greenish, at which point you will know it's time to load the solder. you'll get the idea after half a dozen times.
    (i worked as a plumber's mate for a year.)

    Thanks for the warnings, I'm glad to have a real plumber respond. Since this project, I have purchased a pipe cutter like the one you've shown. But of course, since I bought the proper tool for the job, I haven't had the chance to use it. I'm planning to remodel my kitchen, so I'm sure it'll get used this year. I should have given more warning about being careful with clamping. I was really careful not to put much pressure on the pipe w/ the vise grips. But I'll take your words of caution and find a better way to hold the pipes down while soldering. What do you use for this? I'm lucky enough that these joints haven't leaked ...yet.

    These work great on the outside of the pipe, and inside of the fitting.


    i'll usually just sit something handy that's heavyish that won't melt or burn on top of the pipe - a wrench or piece of 2x4 works fine. longer pieces of pipe tend not to move around so much, so they don't need much. the other thing is that you're often soldering while pipes are in their finished place, so they're held by the fittings on the existing pipe. have fun doing your kitchen - it's pretty rewarding being able to something like this yourself, and it gets easier every time you do it.

    No, you want the pipe to be rough, on the ends, not the whole pipe. Think about it, when you paint something you sand it to rough it up, so that the paint will stick. I have been a plumber for 20 years, so I would know. If you sand it shiny, it will have no surface to grab onto.

    Umm... I'm a licensed plumber as well (as is my father) and I think you're mis-explaining the purpose of this step. You need to CLEAN the inside of all fittings and the tips of the pipes that will be going into the fittings with an emory cloth or coarse sandpaper (for folks who aren't plumbers) and the net result should be that the metal will appear "shiny" (as opposed to the dull oxidized copper look that pipes get once they've been installed for some time) but you do not want to actually POLISH the metal. it's an important distinction because getting to the "shiny" stage is a useful rule of thumb for someone who is trying to clean fittings or pipes. Ideally it should be something close to the lighter reddish-orange copper color that you seen in newer fittings and pipe, but you should also see lines/scratches from the coarse sanding. It's also a useful habit to get into even with new (i.e. shiny) pipes and fittings because those can have non-obvious gunk on them that could negatively affect the quality of the soldered joint. As a rule of thumb I lightly sand even brand new fittings (and of course I thoroughly clean older materials) just in case (I'd rather spen a little extra effort then than a lot of extra effort later tearing a hole in my wall to fix a leak).

    hmmm - have been very successful using scotchbrite on smaller joints (15mm - 22mm) (1/2" and 3/4") and +- 60 roughness sandpaper on the larger sizes. Primarily the use is to get rid of oxidation (which the flux should assist with). Not sure why you're reaming the inside of the pipe - maybe because you've distorted the pipe by cutting with the angle grinder, but your inner tube bore won't interfere in the joint - just get rid of the burr and you should be ready to go (assuming the pipe hasn't heavily lost shape in cutting).

    The reason you ream or deburr the inside of the pipe is basically to allow for a "smooth", uninterrupted flow of the fluid (remember that gases are fluid in a gaseous phase) through the pipe. If you have burrs on the inside of the pipe where you have cut it, you are going to have eddies forming around those burrs resulting in what in aerodynamics/hydrodynamics/fluid dynamics is referred to as drag. Drag ultimately reduces the effiency of the flow of the fluid in the joint which in general plumbing is not a big issue, however in piping where you have a less dense medium (fluids in a gaseous phase) or where you require super accurate pressure at the end point (as in aircraft hydraulic systems) this becomes critical.

    I reamed it to get rid of any oxidation/dirt/grease on the inside of the pipe. There was no appreciable distortion using the grinder.